Troubleshooting Traces Functionality with Langchain's ConversationalRetrievalQAChain

Hi team, I am trying to use the traces functionality with langchain, currently I am using the ConversationalRetrievalQAChain from langchain to obtain responses, on adding tracer as a callback to this, I am getting the following error: I'm not able to find out the exact reason for this issue, any help would be greatly appreciated!